The invention relates to a supply circuit for a piezo-electric motor, for example, of the free progressive wave type schematically represented in FIG. 1 and comprising a rotor 1, driven by friction by a stator 2 which is energized by a piezo-electric element 3.
According to a well-known implementation shown in FIG. 2, the piezo-electric element 3 comprises two piezo-electric areas 5 and 6 disposed in series and alternately polarized. These two areas 5 and 6 are separated by two spaces, neither of which receive an active piezo-electric area: a first space 8 usually serving as sensor in the vibration control loop, and a second neutral space 10. The non-illustrated rear face of the piezo-electric element is connected to the ground 9. The area 5 is energized by a first electrode 11 supplied by a high frequency voltage V.sub.1 ', and the area 6 is energized by a second electrode 12 supplied by a high frequency voltage V.sub.2 ', said tensions V.sub.1 ' and V.sub.2 ' being phase shifted by substantially 90.degree., and supplied by two alternating supply sources independently created from a DC source. The voltages V.sub.1 ' and V.sub.2 ' applied to each of the electrodes cause vibrations in each of the areas 5 and 6, creating two stationary waves whose resultant leads to a free progressive wave resulting in elliptical movements of material points of the elastic element of the stator put in contact with the rotor, which engenders the rotational movement of the rotor with respect to the stator.
The alternating supply sources are thus created by independent supply devices. Such supply devices utilize either two independent magnetic circuits as is described in patents U.S. Pat. No. 5,130,619 and U.S. Pat. No. 5,021,700, or by several independent switches as is described in patent U.S. Pat. No. 5,179,311. These supply devices thus comprise a great number of elements which considerably increases the cost price of such devices, as well as their size.